Different bellhousings are used to connect
a W50 gearbox to an R or M series engine.

Different bellhousings are used to connect
a W55 gearbox to an R or T series engine.

Alloy W5# gearboxes are interchangeable
with each other.

Alloy and steel W5# gearboxes are not
interchangeable with each other.

W50 bellhousings do not fit the W55
gearbox and vice versa.

W55 bellhousings do fit the W56, W57 and
W58 gearboxes and vice versa.

All W## gearboxes after 1970 had the same
output spline as the A## automatic gearboxes.

The following article is taken straight out
from:
"Performance Build Ups, Volume 9, Issue 1"

18R TOYOTA
FOUR-SPEED:

This is a heavy-duty 4spd that was used in 4
and 6 cylinder motors in 18R Coronas, Mark 2 Coronas, 6 cylinder
Cressidas and Crowns. They're available with two different stick
positions. The one in Pic 3 has the kickback shift level and the other
version has the lever 2.5 inches further forward. They're very strong
and won't break behind a 6. A lot of people use them behind V8's quite
successfully and, even if you do break one in such an application, they
can be found at wreckers for as low as $50, which makes it economical to
simply remove the damaged one and fit a replacement. Some people scoff
at these boxes because they were used behind 4 cylinder engines, but a
closer examination reveals they're ridiculously over-engineered for such
an application. If your clutch ever fails, one of these boxes will get
you home quite happily as long as you don't need reverse.

TOYOTA
FIVE-SPEED:

This is the same as the 4 spd
version but you'll note that the rear housing, which contains fifth and
reverse, is bulkier. All the details about the position of the shifter,
the tailshaft yoke and the bolt-up pattern are the same as for the 4 spd.
In the trade, they're commonly known as a steel-case Toyota. They came
on 18R, or 2 litre engines in hatchback or mustang lookalike Celicas.
They were also used in 6 cylinder Coronas and imported Crowns and in
these applications they were fitted with a heavier-duty needle roller
bearing in the front cluster. Unfortunately, you can't tell if this is
the case until you pull it apart, but if you do and you find the roller
bearing, you know the box has been in a 6 cylinder, a turbo model, or a
diesel. Hopefully, you'll find a ball bearing which indicates that is
was fitted to a NA 4 cylinder and has had much less power put through
it. Finding the lower rated box and refitting it with the stronger
roller bearing is ideal. They come in 3 first gear ratios. Versions
fitted to the 18RG engines, which were Yamaha headed engines, were
fitted with a 3.0:1 ratio, which is very high. These versions are fairly
rare but can still be found if you look hard enough. There are also
3.25:1 and 3.5:1 versions available. As with the 4 spd, people fit them
to V8's, but its not a great idea because, unlike the 4 spd, they're
quite expensive ($400). A better choice is the Supra, which is stronger
and doesn't cost much more.

TOYOTA SUPRA FIVE-SPEED:

W58 gearbox - note the steel
sandwich plate
These boxes first appeared in Australian 1984 in the 4 cylinder Corona.
They were also fitted to Celicas and, obviously, Supras. Both 4s and 6s
had exactly the same version, so everything said about using 4 cylinder
Toyota 5 spd units applies to the Supra box. There was at least 4 ratios
in them, starting with an extremely low 4.0:1, which was fitted to
commercial vehicles, following by 3.7, 3.5 and 3.28. They have the same
length input shafts as the other Toyotas and are virtually
interchangeable with the steel-case. However, they do have a different
bolt pattern. As is commonly known, these boxes are extremely strong.
They're much stronger than a steel-caseToyota. Straight from a wreckers,
this box will cost about $500, but a stripped and checked version is
about $700.
There is another, extremely rare and much stronger, version of this box
that was fitted to a 3.0 litre Twin Turbo. Its about half as big again
as a normal Supra but apart from that it looks the same. It has been
known to handle in excess of 550HP with no difficulties. If you can find
one, you'll have to pay something like $1500-$2000, but they are very
rare.
The Supras' shifter also came in 4 different locations:
The above transmissions feature a range of gearshift positions as
standard. Measured from the front face of the transmission these are :
18, 20, 21, 21.5 inches.

The multiple shifter housing
positions of the W58 gearbox. the ma61 stock position is seen second
from the left.

*******On this website I am sharing the
things I find out along the way. I do not guarantee that these
modifications will work on your specific vehicle, any damages caused as
part of the installation or use of these modifications are the the
responsibility of the person who performed the installation.